Phosphoric acid may be used as an etchant in semiconductor processing to selectively etch silicon nitride over silica from silicon process wafers. A build up of dissolved silica in the phosphoric acid etch bath from the etching of wafers, may inhibit further etching of silica from the wafer and thus increase the selectivity of the etchant. However, as the silica content of the etchant bath reaches saturation concentrations, the build up of solid silica precipitate may require the complete exchange of etchant from the bath system to avoid damaging pumps, filters, and other components. Replacement of the phosphoric acid in the bath with fresh acid requires a “seasoning” period to bring the silica concentration in solution back up to levels associated with high selectivity, where during this “seasoning” period the etch bath has low selectivity and thus low efficiency for etching silicon nitride. The use of purchased “preseasoned” acid solutions is costly in terms of both materials and the increased complexity of separate handling equipment. There exists a need for a cost effective method for replenishing etching baths with minimal impact on process complexity.